Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td	(revision 218382)
+++ include/clang/Basic/DiagnosticGroups.td	(working copy)
@@ -146,6 +146,8 @@
 
 def CXX11Narrowing : DiagGroup<"c++11-narrowing">;
 
+def CXX11WarnOverrideMethod : DiagGroup<"warn-missing-override-on-overriding-method">;
+
 // Original name of this warning in Clang
 def : DiagGroup<"c++0x-narrowing", [CXX11Narrowing]>;
 
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td	(revision 218382)
+++ include/clang/Basic/DiagnosticSemaKinds.td	(working copy)
@@ -1683,6 +1683,9 @@
   "%select{function|functions}1">;
 def err_function_marked_override_not_overriding : Error<
   "%0 marked 'override' but does not override any member functions">;
+def warn_function_marked_not_override_overriding : Warning <
+  "%0 is not marked 'override' but overrides a member functions">,
+  InGroup<CXX11WarnOverrideMethod>, DefaultIgnore;
 def err_class_marked_final_used_as_base : Error<
   "base %0 is marked '%select{final|sealed}1'">;
 def warn_abstract_final_class : Warning<
Index: include/clang/Sema/Sema.h
===================================================================
--- include/clang/Sema/Sema.h	(revision 218382)
+++ include/clang/Sema/Sema.h	(working copy)
@@ -5070,6 +5070,10 @@
 
   /// CheckOverrideControl - Check C++11 override control semantics.
   void CheckOverrideControl(NamedDecl *D);
+    
+  /// DiagnoseAbsenseOfOverrideControl - Diagnose if override control was
+  /// not used in the; otherwise, overriding method.
+  void DiagnoseAbsenseOfOverrideControl(NamedDecl *D);
 
   /// CheckForFunctionMarkedFinal - Checks whether a virtual member function
   /// overrides a virtual member function marked 'final', according to
Index: lib/Sema/SemaDeclCXX.cpp
===================================================================
--- lib/Sema/SemaDeclCXX.cpp	(revision 218382)
+++ lib/Sema/SemaDeclCXX.cpp	(working copy)
@@ -1895,6 +1895,27 @@
       << MD->getDeclName();
 }
 
+void Sema::DiagnoseAbsenseOfOverrideControl(NamedDecl *D) {
+  if (D->isInvalidDecl())
+    return;
+  CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(D);
+  if (!MD || Diags.isIgnored(diag::warn_function_marked_not_override_overriding,
+                             MD->getLocation()))
+    return;
+  bool HasOverriddenMethods =
+    MD->begin_overridden_methods() != MD->end_overridden_methods();
+  if (HasOverriddenMethods) {
+    Diag(MD->getLocation(), diag::warn_function_marked_not_override_overriding)
+      << MD->getDeclName();
+    for (CXXMethodDecl::method_iterator I = MD->begin_overridden_methods(),
+         E = MD->end_overridden_methods(); I != E; ++I) {
+      const CXXMethodDecl *OMD = *I;
+      Diag(OMD->getLocation(), diag::note_overridden_virtual_function);
+      break;
+    }
+  }
+}
+
 /// CheckIfOverriddenFunctionIsMarkedFinal - Checks whether a virtual member
 /// function overrides a virtual member function marked 'final', according to
 /// C++11 [class.virtual]p4.
@@ -2182,6 +2203,9 @@
 
   CheckOverrideControl(Member);
 
+  if (LangOpts.CPlusPlus11 && !Member->hasAttr<OverrideAttr>())
+    DiagnoseAbsenseOfOverrideControl(Member);
+
   assert((Name || isInstField) && "No identifier for non-field ?");
 
   if (isInstField) {
Index: test/SemaCXX/cxx11-warn-missing-override.cpp
===================================================================
--- test/SemaCXX/cxx11-warn-missing-override.cpp	(revision 0)
+++ test/SemaCXX/cxx11-warn-missing-override.cpp	(working copy)
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -Wwarn-missing-override-on-overriding-method -verify -std=c++11 %s
+// rdar://18295240
+
+struct A
+{
+    virtual void foo(); // expected-note {{overridden virtual function is here}}
+    void bar();
+    virtual void gorf() {} // expected-note {{overridden virtual function is here}}
+    virtual void g() = 0; // expected-note {{overridden virtual function is here}}
+};
+
+struct B : A
+{
+    void foo(); // expected-warning {{'foo' is not marked 'override' but overrides a member functions}}
+    void bar();
+};
+
+struct C : B
+{
+    virtual void gorf() {} // expected-warning {{'gorf' is not marked 'override' but overrides a member functions}}
+    virtual void g() = 0; // expected-warning {{'g' is not marked 'override' but overrides a member functions}}
+};
Index: test/SemaCXX/virtuals.cpp
===================================================================
--- test/SemaCXX/virtuals.cpp	(revision 218382)
+++ test/SemaCXX/virtuals.cpp	(working copy)
@@ -1,8 +1,9 @@
-// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -verify -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -Wwarn-missing-override-on-overriding-method -verify -std=c++11 %s
 
 class A {
   virtual void f();
-  virtual void g() = 0; // expected-note{{unimplemented pure virtual method 'g' in 'A'}}
+  virtual void g() = 0; // expected-note{{unimplemented pure virtual method 'g' in 'A'}} \
+			// expected-note {{overridden virtual function is here}}
 
   void h() = 0; // expected-error {{'h' is not virtual and cannot be declared pure}}
   void i() = 1; // expected-error {{initializer on function does not look like a pure-specifier}}
@@ -19,7 +20,7 @@
 
 class B : public A {
   // Needs to recognize that overridden function is virtual.
-  void g() = 0;
+  void g() = 0; // expected-warning {{'g' is not marked 'override' but overrides a member functions}}
 
   // Needs to recognize that function does not override.
   void g(int) = 0; // expected-error{{'g' is not virtual and cannot be declared pure}}